1. Field of the Invention
The invention relates to the field of industrial wastewater purification, and more particularly to a device and a method for sewage treatment using variable magnetic field. The device and method are especially suitable in low temperature conditions for strengthening the biological treatment of the food industry wastewater.
2. Description of the Related Art
Biological treatment of food industry wastewater is typically adopted. However, temperature has an influence on the growth, reproduction, metabolism, species distribution and population size of microorganisms, which further affects the sewage treatment efficiency. In addition, the temperature has a great influence on the flocculation properties of activated sludge and viscosity of wastewater.
With the increasing strictness of sewage treatment standards, conventional methods for food industry wastewater treatment cannot meet the requirements. Particularly, under low temperature conditions, the metabolism ability of the microbe decreases, so does the chemical reaction rate. Thus, the biological treatment of wastewater runs at a low efficiency.
Studies show that a certain magnetic field strength can improve the removal rate of water pollutants chemical oxygen demand (COD), ammonia nitrogen and nitrate nitrogen. Specifically, the magnetic field strength of between 90 and 120 mT can improve COD removal efficiency significantly and the strength of between 30 and 60 mT can promote removal of ammonia nitrogen. The magnetic field also has an obvious effect on the aerobic denitrification process. Within the range of between 0 and 150 mT, the increase of the magnetic field strength improves the nitrate nitrogen removal. However, combining low temperature and magnetic field to treat food industry wastewater has not yet been reported.